A 79-page FBI dossier released on George Orwell reveals how the British author of Animal Farm and 1984 was used by both the Americans and the Russians as a key figure in the battle for ideas for two decades after his death in 1950.

Even before 1984 was published in 1949, US publishers sought to exploit the novel as an attack on Soviet totalitarianism by seeking the endorsement of J Edgar Hoover, the FBI chief - ironically, he was later dubbed America's Big Brother.

A decade later the Soviets used Orwell as part of a smear campaign to tell the Russian people that his satire was based on real life in America where everybody was under survellience.

In the 1960s and 1970s the US security services monitored George Orwell societies and film clubs on US campuses to make sure they were not a cover for subversive pro-socialist behaviour. His name was even linked with "Americong", a terrorist group which bombed an officers' mess at an air force base in Denver, Colorado, in 1972 in protest at the war in Vietnam.

Details of the file have been released under the US freedom of information act but 11 pages remain under wraps. FBI reports about the author have been heavily censored, even though some were delivered three years after Orwell's death.

The file, opened by Hoover himself, begins with a letter from Orwell's publishers in April 1949, saying: "We hope you might be interested in helping to call this book to the attention of the American pub lic - and thus, perhaps, helping to halt totalitarianism".

Eugene Reynal, the vice-president of the publishing firm Harcourt Brace, added: "1984 is an important book because it provides a picture of a plausible but frightening extension of present social and political trends. Orwell brings home to the reader in a story of mounting interest the horrors of a totalitarian world can and may bring to us within less than two generations."

He goes on: "The book leaves the reader with the shocked feeling that there is not single horrible feature in the world of 1984 that is not present, in embryo, today.

"It describes the process by which the last man in whom the spark of human spirit has not been totally suppressed, comes to believe, literally, that two plus two equals five."

The 1955 British-made animated version of Animal Farm thrilled the FBI, who declared that it had "hit the jackpot".

Hoover declined to endorse 1984 and he ordered files kept on the author - including book and film review cuttings. A heavily censored agent's report says that Orwell had originally been "sympathetic toward the communists but he later turned against them".

Ten years later the FBI was reporting on a " smear campaign" organised in East Berlin claiming that Orwell's satire was based on real life in America "where police survellience and investigation has surpassed the world and had no equals.

"Already today an American lives, so to speak, under a glass cover, and is viewed from all sides," said a report which was distributed across the communist world.